Deformation of Natural Pyrope at Mantle Conditions

Garnet is an important mineral existing widely from the lithosphere to the upper mantle, which is the third most abundant phase in the upper mantle and the second most important phase in the transition zone. Garnet is also one of the two major phases in eclogite. Pyrope is one of the most important endmembers in the garnet family. It is a mantle garnet and is unstable at low pressure and high temperature (e.g. <2 GPa and at 1673K). Due to the technique limits, the direct deformation data of pyrope at steady state is sparse in the literature up to now. We perform several deformation experiments of natural pyrope at high pressure and temperature on a deformation-DIA (DDIA) apparatus, Sam85, at X17B2, NSLS. Polycrystalline powder samples are used. Samples are pressurized at room temperature first and then are annealed at 1200°C for at least 2 hours before deformation. Total strain is in-situ measured from the radiographic technique. At constant strain rate (~10-5-10-7s-1), differential stress is obtained from the elastic strain derived from the in-situ x-ray diffraction data of the sample using a 10-element solid state detector system at different pressures and temperatures, by which the stress precision is 10 MPa. Data indicate a large strain hardening regime with steady state stresses higher than that of San Carlos olivine. A flow law equation is derived.